Ultra high frequency system



n 2 Sheets-Sheet l July 16, 1946. J. R. wHlNNERY ULTRA HIGH FREQUENCY SYSTEM Filed oet. 51, 1942' inventor: John RWhirmeT y His 'Attorney July 16', 1946. J. R. WHINNERY ULTRA HIGH FREQUENCY SYSTEM Filed Oct. 51, 1942 2 Sheets-Sheet 2 Invent or; do'hn R. Whimery,

y )gw/Attorney Patented July 16, 1946 UL'rnA man FREQUENCY SYSTEM John R. vWhinnery, Schenectady, N. Y., assigner to General Electric Com New York pany, a corporation of Application October 31, 1942, Serial No. 464,037 Y Claims. (Cl. 315-39) My invention relates to ultra high frequency systems and more particularly to electric discharge devices and associated space resonant cavities, orv regions, for the production and utilization of ultra high frequency energy.

Energy may be transmitted dielectrically through wave guides of the hollow-pipe type vwhen the frequency at which the guide is excited is greater than a critical minimum or cut-off fre-4 quency, the energy being transmitted through the dielectric of the medium within the guide and conductive or metallic defining members or walls of the guide ser-ving to direct the propagation of the electromagnetic wave.

The types of waves which may be transmitted dielectrically through guides of this nature are y manifold and have been classied in the early stages of the development of this art into E and H type waves; At a somewhat later date, the terms transverse magnetic (TM) and Vtransverse electric l(TE) have been'used to define the E and H type waves, respectively. In the E type wave, or the transverse magnetic type, the,`

electromagnetic waves have both longitudinal and transverse components of electric field, but only a. transverse component of magnetic field. By the use of the word transverse is meant transverse to the direction of wave propagation through the guide. In the H type waves, or the transverse electric type waves, the electromagnetic waves have both a longitudinal and a transverse component of magnetic field, but only a transverse component of electric field. Waves transmitted through guides of this nature have been identified by the use of the subscripts, as indicated, En,m and Hmm. 'I'he subscript n indicates the order and the subscript m indicates the mode of propagation. For` example in circular guides, the order of the Waves is determined by the manner in which the field intensity varies circumferentially around the axis of the guide, whereas the mode is determined by the manner of its variation with distance from the axis of the guide. Although hereinafter in the discussion of my invention an H01 type wave in a rectangular guide will be referred to, ity is to be ap-- preciated that my invention is applicable with equal facility to other H type waves as well as E type waves.

It is an object of my invention to provide new and improved ultra high frequency space 'resonant devices. v

It is'another object of my invention to provide,

in connection with high frequency' electric discharge devices.

. lators.

It is a still further object of my invention to provide new and improved ultra high frequency space resonant amplifiers.

It is a still further object of my invention to provide newand improved space resonant cavities, or regions, having a'particular conn-guration to facilitate the use therewith of electric discharge 'devices wherein the space resonant regions are formed by employing tuned sections of a dielectric wave guide of the hollow-pipe type and 'wherein the transverse dimensions of the section of the wave guide are chosen in order to compensate for the ,capacitance effect of the electric discharge device so that electromagnetic waves may be propagated therethrough or sustained in a manner substantially unaffected by the presence of the discharge device.

Itf is a still further Yobject of my invention to provide s. new and improved ultra -high frequency system wherein an ultra high frequency triode is positioned within a section of a dielectric wave guide and wherein the wave guide is foreshortened in its width within the vicinity of the electric discharge device in order that the impedance of the guide is substantially uniform along its longitudinal axis.

Brieiiy stated, in the illustrated embodiments .y

of my invention I provide ultra high frequency space resonant systems comprising a tuned section of a dielectric wave guide of the hollow-pipe type which may be used for various purposes, such as for the production of electromagnetic oscillations, or for the amplification of electromagnetic waves of high frequency. The transverse dimensions of the guide are chosen within the vicinity of the electric discharge device so that the guide oifers a substantially uniform impedance along its longitudinal axis. More specically, the transverse dimension or width of .they guide is restricted within the .region of the electric discharge device to compensate for the capacitance effect of the device, thereby mainnew and improved dielectric wave guides for use taining the desired relationship -between the efi'ective distributed inductance and capacitance of the guide not only at points removed from the position of the discharge device but within the vicinity thereof.l l

c 'and 6 represent a 'further modification` of my inanding of my invention, i

ings, and its scope will be pointed out in the v appended claims. Figs.'1 and 2 diagrammati'cally illustrate an embodiment of my invention as applied to an ultra high frequency space resonant system which may be used either as an ultra high frequency oscillator, or as an ultra high fre-A quency amplifier. Figs. 3 and 4 represent a fur- ,ther modification which is provided with coupling means interposed betweenj the anode-grid and c., the grid-cathode space resonantcavities. Figs. 5

vention as applied to a high frequency space resonant system of the re-entrant type, and Fig. '7 represents a modification of the arrangement. shown in Figs. 5 and 6 Awherein a 'double reentrant featureis employed.

Referring now tol Figs. 1 and 2 jointly, 4I have there illustrated my invention .as applied to an ultra high frequency space resonant system comprising a pair of lspace resonant regions, or cavities; I and 2 which are defined by sections of a dielectric wave guide of the hollow-pipe type. These sections/may be defined'by conductive or metallic members constructed of ,copper or brass and, of course, may assume vvarious cross sectional configurations. For the purpose ofillustrating my invention, I -have `chosen to employ dielectric wave guides of rectangular cross section, which may be defined by metallic outer "plates or members 3 and ll, and having an intermediate coxn`- mon metallic member 5 which defines a common metallic boundary between `the two. regions. Members 3 -5 are positioned so that the heights a 'of regions I and 2 are preferably equal, and the width b may be established by means of lateral wall members 6 and l which, of course, arer conductively connected to members 3, d and 5.

In order tov facilitate the/employment of an electric discharge device, to be described presently, in the spaceresonant system, plates 3, il and 5 are provided, respectively, with apertures, preferably circular apertures, .8, 9 and IIJ which are substantially coaxial, the axis of which lies substantially perpendicular to the longitudinal axes 0f the cavities I and 2. v

As a means for establishing the longitudinal dimensions of the cavities tand 2, and as a means for tuning these cavities with'respect to the electromagnetic waves established therein, I employ a plurality of adjustable end-wall members which may take the form of plungers II, I2. 'I3 and It which may be actuated by any suitable mechanical expedient, such as rods l5. .It will be observed-thatplungers II and I2 engage the metallic walls of members 3 and 5 which define space resonant cavity II, and that the plungers I3 and I4 engage the walls of metallic members 4 and' 5 which define the space resonant cavity 2. Prior to a further description of the system, .it is believed that at this time it will be helpful to point out certain fundamental aspects of dielectric wave guides of the hollow-pipe type, with particular attention to rectangular guides. vAs stated above, there is a critical minimum or cutoff frequency for each mode in a dielectric guide, which is determined by the mode,the dielectric constant of the medium within the guid throughv which the electromagnetic waves are-propagated,` and the transverse dimensions of the guide, Below this minimum or cut-off frequency the electromagnetic waves are rapidly attenuated and theenerg'y thereof is not transmitted an apaicaeei c.

4 h'=a+i (1) where a is the attenuation constant and is L10 the phase constant and both are real quantities whose magnitudes depend upon frequency.

If the frequency is sufficiently large, a is very smallv compared to and the wavesare propa- 'gated'without appreciable attenuation at a'phase 15 velocity which is a function of the transverse dimension of the guide. vWhen the excitation frequency is below the critical frequency, the Equation 1 may still be used but a and both become imaginary with the result that p determines the attenuation 'and a determines the extent of wave action. Physically, this means that the transmission of waves through the guide is virtually non-existent at frequencies below the cut-ofi frequency'.

The phase constant may be expressed:

i erger-err wherew is the angular velocity ofthe wave propagated through the guide (w='21rf where f is.

In order to simplify still furtherthe presenta-1 tion of the subject matter relative to a rectangular dielectric wave guide, it will be assumed that the dielectric isair and that the system is arranged for the transmission of an Hoi type .wave where the electric component of the field is perpendicular to the base b. With these assumptions, vEquations 2 and 3 become:

where c is the velocity of light.

A concept of total impedance useful in matching wave'guidessuggests that the impedance ofl the guide remain substantially constant along its longitudinal dimension, and it will of course be observed that there must be a fixed or predeterequation'form as follows:

. in contact pins 33 and 3|.

where Z represents the impedance; a is the permeability of air, and c is the velocity of light.

It the guide impedance is constant, the wave will be propagated or sustained uniformly and to maintain this impedance constant for changes in guide dimensions or changes in-guide characteristi, one must have at any length the following relationship:

%)\,= constant Il k particular. wave adjusted to have longitudinal dimensions equal to a half-wave length, measured in terms of xg, or multiples thereof, so that standing electromagnetic waves are established within these cavities. That is, upon adjustment of plungers |||4 the standing potential and current curves of the electromagnetic waves assume positions fixed in space butv undergoing sinusoidal time variations. More particularly, voltage nodes of the potential curves occur at the end of the cavities, and a cur-- rent node occurs at a point midway between the ends of the cavities. the voltage and current standing waves belngin time quadrature.

I position within the apertures B, 8 and I0 an electric discharge device |8of the type disclosed and claimed in copending patent application Serial No. 436,633 of James E. Beggs, filed March 28, 1942, and which is assigned to the assignee of the present application. This discharge device is peculiarly adapted for the utilization of ultra high frequency energy and comprises a plurality of enclosed electrodes including a cylindrical anode I1, a cylindrical cathode I8 and a grid I8 maintained in spaced relation between the anode and the cathode. Anode |1 and grid I8 are supported by metallic discs 20 and 2|, the latter of which is conductively connected to the intermediate plate member 5 through resilient fingers or an annular metallic collar 22. Cathode I8 is supported by a cylindrical member 23 having a flatl disc part 24 substantially parallel to disc 2|. Members 2I and 23 provide externally accessible high frequency terminals for grid I9 and cathode i 8. Cathode |8 is provided with a flanged part 25 substantially parallel to the lower surface of part 24 and is spaced therefrom by means of an insulator 26 so that the cathode is electrically insu' lated therefrom, so far as direct current potentials are concerned, but effectively connected thereto with reference to high frequency current, by virtue of the electrostatic coupling between the parallel surfaces. Cathode I8 is also provided with a coiled heating element 21 to which current may be supplied through suitable conductors terminated in contact pins 28 and 29.

` Unidirectional potential may be applied to the cathode I8 through other conductors terminated Contact pins 28-3I are supported by a base 32 which encloses a metallic header (not shown) and in which the various conductors for the cathode heating element and the cathode are sealed.

To complete the enclosure for the electrodes of the discharge device and for maintaining the electrodes in spaced relation, there is provided cylindrical vitreous insulators 33 and 34 immediately surrounding the' anode |1 and cathode I8 and which are sealed to members 20, 2| and part 24. vAnmie i1 is electrically insulated from the metallic or conductive structure of the space resonant cavities, and particularly from plate 3, so far as direct current potentials are concerned, by means of an insulator 35, so that a suitable potential may be applied across the anode I 1 and cathode I3 through conductors 36 and 31. The

anode is eliectively connected to the top of cavityI stituting an extension of an inner conductor 48 of. a coaxial or concentric transmission line comprising the inner conductor 40 and an outer tubular'conductor 4|, the latter of which is conductively connected 'to outer member 3 and is arranged toslide along the outer surface thereof. Plate 3 is provided with an opening 42 of appreciable longitudinal dimension, thereby permitting .adjustment of the position of loop 39 to that optimum position wherein maximum energy may be extracted from the space resonant region I. Any suitable mechanical -arrangement may be provided for adjusting loop 39, and such an arrangement is diagrammatically illustrated as constituting a plate 43 welded or soldered to the outer surface of member 3 and which positions and guides the flanged part of outer conductor 4 I.

Where the arrangement illustrated in Figs. 1 and 2 is employed as an amplifier, the input excitation for the grid-cathode space resonant cavity 2 may be provided by means of input electrode means 44 constituting an outer tubular conductor 45 and an inner conductor 46 terminated in a loop 41 whichv projects into the space resonant region 2. It will be understood that other forms of electrode means, such vas probes or the equivaient, may be employed for this purpose.

In order to maintain Ithe impedance of the guide constant along its length and particularly to arrange cavities i and 2 so that the cavities.

oier substantially no discontinuity due to the presence of the discharge device I6, I provide means within the respective cavities for restricting the transverse dimension b within the vicintive cavities are substantially unaiected by the presence of the discharge device. More particularly, the transverse dimension within 'the vicinity of the electric discharge device I6 is foreshortened so that the guide at this point is substantially resonant to the electromagnetic waves which it is desired to sustain. In other words,

inasmuch as the electric discharge device |18 oiiers anappreciable capacitance by virtue of its configuration and presence, the dimension b is foreshortened so that the resultant or eiiective distributed capitance and the capacitance of the discharge device i8 resonate with the distributed y 7; inductance of this portion of-the Vguide or cavities'.

, One way in which this desired symmetry oi.' the longitudinal impedance` of the respective cavitiesv may be obtained is by restricting thetransverse dimension b and by providing the lateral wallv amasar ties. Furthermore.' tuning and coupling may Alie obtained with facility.

members 6 and 7 with appropriately enlarged wall thicknesses or protuberances wand 49 hav ing a curvature and a congura/tion so that no abrupt discontinuityy is encountered4 as the wave progresses along the' longitudinal axis. For example, the protuberances t8 and Il@ may be formed integral with the lateral wall members 6 and 1,' or may be constituted separately and inserted in the proper position. Of course, it is required that these protuberances t8 and 49 be conductiveand be conductively connected to the wall members t and 1. Where the protuberances'l are constructed separately, these parts. may be Upon the application of a suitable potential,V

such as a unidirectional potential, to the anode I1 and cathode I8, the space resonant system shown in Figs. l and 2 are initiated in operation. Each of the cavities I and 2 is tuned or resonant to the desired frequencyl and energy is supplied to an external utilization circuit from the anodegrid cavity through loop 39 and the concentric transmission line comprising conductors dll and In the arrangement of Figs. 1 andv2, when used as an oscillator, the coupling between the anode-grid cavity I and the grid-cathode cavity 2 is obtained principally by virtue of the interelectrode capacitance effects of the electric discharge device I6, whereby the systemy is maintained in oscillation by virtue of the cyclic variations in the potential impressed between grid I9 and cathode I8. Inasmuch' as the grid and The arrangement of Fig. u1 maylalso be employedas an amplifier or ultra high frequency voltages orcurrents, in which case the input electrode means, and particularly loop tl, is energized. through the concentric transmission line tt, establishing vwithin the grid-cathode space resonant region 2 an electromagnetic oscillation. In this case, of course, the cavity 2 being tuned l, to the irequency of the input excitation sustains is positioned within the vicinityof the ps1-,enum

maximum of this standing wave, the grid and the cathode undergo cyclic variations of potential to modulate the electron beam transmitted bet tween `anode Il and cathode i8, consequently eiecting energization ofthe anode-grid cavity I and maintaining this cavity in oscillation.

Energyl is vextracted from the anode-grid cavity the boundary member 5 are common to the two cavities. it may be considered that the anode and cathode voltages vary substantially in that phase` cavities, resonance is then determined by an electromagnetic wave traveling essentially in the transversedirection Within the vicinity of the discharge device I6, due to the fact that the ca.-

'3l by loop 39 and the associated concentric transmission line. The ampliication of the input signal is obtained by virtue of the amplication edect due to the electric discharge device I6 which couples the respective cavities.

Figs. 3 and 4 show a further embodiment of my inventlon.simi1ar in many respects to that shown in Figs. l and 2, and corresponding elements have been assigned like reference n`umerals. In the arrangement of Figs. 3 and 4, there is provided separate lcoupling means, such as a, probe 50,. supported by the intermediate metallic member 5, but spaced electrically therefrom by means of insulating glass bead or seal 5|. Other suitable formsof coupling means may be employed and, of course. positioned at that point to obtain the maximum or desired coupling eil'ect.

Figs. 5 and 6 represent a further modication of` my invention which is similar in many re spects to that shown in Figs. 1 and 2, and corresponding elements have been Aassigned like reference numerals. In the arrangement of Figs. 5 and 6, I provide a space resonant oscillator of the re-entrant type wherein an intermediate member 52, dening the common boundary be' tween the anode-grid and the grid-cathode space resonant cavities. does not extend the entire longitudinal dimension of the respective cavities, so

f that there is afforded a re-entrant coupling path pacitance loading eifect thereof tends to lower the natural resonance frequency within that 'region to a frequency for which the width b is less vthan anali-wave length.' Consequently, the low- 53 between the anode-grid cavity I and the gridcathode cavity 2 thereby constituting a feed-back connection between these. two cavities. When such a construction is employed. the corresponding end walls of the respective cavities may comprise a single tuning plunger 5t which engages the'inner surfaces ofthe metallic dening members 3, t, E Vand 6.

electromagnetic fields of the cavities by loops or lines in regions of the cavities far from"y the discharge device are not effective under those conditions.

By -the restriction of the transversedimension,

or dimensions, of the cavities within the vicinity of discharge device I6, the tendency to establish a localized wave region, or a -wave ,propagated along the transverse axis withinthe vicinity'of the discharge device is reducedv 'or substantially eliminatedand the electromagnetic waves will` be sustained symmetrically throughout the en-v tirelength oi' the respective space resonant cavi- .N trated a still further modiilcation of my inven- In the arrangement of Figs. 5 and 6, thalength of the member 52 is preferably chosen so thatA the desired phase relationship between the anode-grid and the grid-cathode voltages is maintained. Forexample, since the grid I9vis at the common potential, in order that the anode and cathode vary in the proper phase relationship, the axial or longitudinal dimension of the member 52 should be substantially equal to a half-wave length of the electromagnetic waves sustained within ,the respective 1 cavities. Od

` course, actually the `physical length ofthe part 52 is somewhat less than a half-wave length due to the end effects.

`In the arrangement of 7 there is illusftion as applied to a space resonant system, such as an ultrav high frequency oscillator employing a double re-entrant feature. That is. the anodegrid and the grid-cathode cavities are donned by a metallic member having parts 55 and 56 which a single member having' therein an aperture" through which the discharge device I extends. Members 55 and 55 extend axially the longitudinal dimension of the system, but'do not engage the metallic endynwalls defined by plungers 58 andl 59, thereby aifording coupling paths -GII and- 6I between the` anodemay be constituted by grid and the grid-cathode spaceresonant regions.

Energy is fed back'from the anode-grid cavity to the grid-cathode cavity, and the axial dimensionsof the parts 55 and 55 are chosen in order that 'the grid-cathode voltage have the desired phase yrelationship to maintain the system in oscillation. p l

While I have shown and described my invention as applied to partic'ular systems and as ern-'- bodying various -devices diagrammatically shown,

1. A space resonant system comprising a sec- I tion of a dielectric wave guide of the hollow-pipe type including conductive defining walls, said section being dimensioned to support electromagnetic waves of predetermined frequency, an electric discharge device comprising a plurality of enclosed electrodes connected to oppositely disposed walls-.of said guide and being positioned substantially transverse to the longitudinal axis of said section and enclosing structure for said electrodes, and means for restricting a transverse dimension of said guide within`-` the vicinity of said device to compensate for the capacitance eifect of said discharge device in order that the electromagnetic wave of said predetermined frequency is substantially unaffected by the presence of said discharge device.

2. A space resonant system comprising a section of a dielectric wave guide of the hollow-pipe type including conductivewalls, said section being excited at a frequency greater than the cut-off frequency and having `dimensions so that said section'is tuned substantially to the excitation frequency, an electric discharge devicecomprising a plurality of enclosed electrodesconnected to oppositely disposed walls of said section, an enclosing structure for said electrodes, and means for restricting a transverse dimension of said guide to compensate for the capacitance effect Aof said discharge device in order that the wave of v section to compensate for the capacitance eii'ect of said discharge device in order that the electromagnetic wave of said predetermined frequency is substantially unaffected by the presence of said discharge device, and electrode means associated-with said section for supplying energy the capacitance eil'ect of said discharge device in order that the electromagnetic wave ofl said predetermined frequency is substantially unaffected by the presence of said discharge device, and output electrode means connected to said section.

5. An ultra high frequency space resonant system comprising a section of a dielectric wave guide of the hollow-pipe type defined by longitudinal and lateral conductive members, said sec.. tion being excited at a predetermined frequency correlatedV to the dimensions of said section, and

-an electric discharge device including a plurality of electrodes comprising'an anode, a cathode and a grid, transverse discs for supporting said members and for providing high frequency terminals between two of said electrodes and the conductive members of said section and an enclosing structure for said electrodes, the transverse dimension of said section being restricted within the vicinity of said electric discharge device in order to compensate for the capacitance effect of said discharge device.

6. A high frequency space resonant system comy prising a section of a dielectric wave guide of the hollow-pipe type including a conductive member for deining a space resonant region, said space resonant region being excited at a frequency corresponding to the natural frequency thereof, and an electric discharge device including an electric dischargev path provided by a pair of electrodes `and lan enclosing structure therefor, said discharge device being connected transversely across said guide along the longitudinal axis thereof within the vicinity of the potential maximum of the standing electromagnetic wave within said region, means for restricting the section of said said excitation frequency is substantially unaffected by the presence of said discharge device.

3. A space resonant system comprisinga section of a dielectric wave guide of the hollowfpipe typeinciuding a metallic defining member, said section being dimensioned to support electromagnetic waves of apredetermined frequency and having dimensionsso that said section is tuned substantially to said frequency, an electric discharge .device comprising a pair of enclosed elec trodes, an enclosing structure immediately surrounding said electrodes and providing externally accessible high frequency terminals connected to oppositely disposed points of said member, means for restricting a transverse dimension of said electric wave guide within the vicinity of said discharge device to compensate for the capacitance eifect of said electric discharge device.

7. A high frequency space resonant system comprising a pair of space resonant cavities defined by a pair of sections of a dielectric wave guide and having a common metallic boundary, an electric discharge device comprising a plurality of enclosed electrodes including an anode, a cathode and a grid and an enclosing structure therefor, said discharge device being positioned within said cavities and having the cathode and grid thereof connected to oppositely disposed transverse points of one of said cavities, and means for restricting the width of said cavities within the vicinity of said electric discharge device in order to compensate for the capacitance effect thereof.

8. An ultra high frequency space resonant system comprising a pair of space resonant cavities defined by two/adjacent sections of a dielectric- Monaci 1 form impedance wave guide ci the hollow-pipe type including conductive cuter defining members and having' a commonmetallic boundary, said members being provided with alined apertures qthe axis of whichA is substantially perpendicular to the longitudinal axis of said cavities, an electric discharge device positioned within said apertures and comprising a plurality of enclosed electrodes including an anode, a cathode and a grid and an enclosing along the longitudinal axes.

9. An ultra high frequency space resonant oscillator comprising a pair oi' space resonant cavities defined by two adjacent sections of a dielectric wave guide of the hollowpipe type including conductive outer defining members and having a common metallic boundary, said members being provided with apertures alined substantially perpendicularly to the longitudinal a lof said cav- -io structure for said electrodes, said anode being tromagnetic waves of a predetermined frequency v ities, an electric discharge device positioned within said apertures and comprising a plurality of enclosed electrodes including an anode, acathode and a grid and an enclosing structure immediately surrounding said electrodes and having externally accessible high frequency terminals, said anode`being electrically insulated from one of the outer members and said grid and said cathode being connected respectively to the common metallic boundary and the other outer member, means for applying a potential across said anode and cathode, means for restricting the width of said cavities within the vicinity of said electric discharge device in order to compensate for the capacitance edect thereof wherebyA said cavities adord a substantially uniform impedance to electromagnetic waves of a predetermined frequency along the longitudinal axes, and output electrode means connected to the cavity associated with the anode-grid circuit of said discharge device.

10. An ultra high frequency space resonant oscillator comprising a pair of space resonant cavities dened by two adjacent sections of a dielectric wave guide of the hollow-pipe type including conductive outer defining members and having a common metallic boundary, said members being provided with substantially concentric apertures. alined perpendicular to the longitudinal axis of said cavities, an electric discharge device 'positioned within said apertures and comprising a plurality of enclosed electrodes including an anode, a cathode and a grid andan enclosing structure immediately surrounding said electrodes and having externally accessible high frequency terminals, said anode being electrically insulated from one of the outer members and said grid and said cathode being connected respectively to the common metallic boundary and the other outer member, means for applying a potential across said anode and cathode, means for restricting the width of said cavities within the vicinity of said electric discharge device in order to compensate for the capacitance eil'ect thereof predetermined frequency along vthe longitudinal axes, outputelectrode means lconnected tothe cavity associatedwith the anode-grid circuitof said discharge device, and means for ltuning at least one. of said cavities. f g

11. An ultra high frequency space resonant amplifier comprising a pair of space resonant cavities deilned by two adjacent sections of al dielectric wave guideof the hollow-pipe type including conductive' outer vdening members and having' a common metallic boundary, said mem-l bers being provided With concentric apertures the ams of which is substantially perpendicular to the longitudinal axis of -said cavities, an electric discharge device positioned Within said apertures and comprising a plurality of electrodes including an anode, a cathode and a grid and an enclosing structure immediately surrounding said electrodes and adording ,externally accessible high frequency terminals thereto, said anode Y being electrically insulated-from one of said outer members and said grid and said cathode being connected respectively to the common metallic `boundary and the other outer member, means for applying -a'potential across said anode and said cathode, means for restricting the width ofl said cavities within the vicinityI of said electric discharge device in order to compensate for' the capacitance efiectthereof whereby said cavities adord a substantially uniform impedance to electromagnetic waves of a predetermined frequency along the 4longitudinal axes, input electrode means associated with the cavity connected ,to said grid and said cathode, and output electrode means associated with the'othercavity.; 12. An ultra high frequency space' resonant system comprising a pairof space resonant cavities deiined by two adjacent sections of a dielectric wave guide of the hollow-pipe type'including outer defining members vand having throughout an appreciable longitudinal length thereof a common `metallic boundary, of the re-entrant type whereby energy may be transferred between said cavities, an electric discharge device posi- `tioned within apertures of said outer members and'said common metallic boundary and comprising a pllnality of enclosed electrodes including an anode, a cathode and a grid and an enclosing structurer surrounding said electrodes, said anode being electrically insulated from one of the outer members and said grid vand said cathode being connected respectively to the common metallic boundary and the other outer member, means for lapplying a potential across said anode and said cathode, means for restricting the width of said cavities within the vicinity of said electric discharge device in order to compensate for the capacitance effect thereof so that saidl cavities afford a substantially uniform impedance to electromagnetic waves of a predeter- `mined frequency along the longitudinal axes thereohmeans for tuning at least one of said cavities, and means for extracting energy from quencyterminals thereto, a pair yoi space reso-p nant cavities .defined by two adjacent sections of vwhereby said cavities adord a substantiallyuni- 'it a dielectric wave guide of the hollow-pipe typt*v to electromagnetic waves of a including outer defining members and an intermediate member, said intermediate member being connected to said grid through the associated terminal but not extending the entire axial length of said cavity thereby providing a re-entrant path for the transfer of energy from the anode-grid to the grid-cathode circuit of said discharge device, means for restricting the width of said cavities within the vicinity of said electric discharge device in order to compensate for the capacitance eiect thereof so that said cavities afford a. substantially uniform impedance to electromagnetic waves of a predetermined frequency along the longitudinal axes, and electrode means associated with one of said cavities.

14. An ultra high frequency space resonant system comprising an electric discharge device including a plurality of enclosed electrodes including an anode, a cathode and a grid and an enclosing structure surrounding said electrodes, a pair of space resonant cavities defined by two adjacent sections having a dielectric wave guide of the hollow-pipe type including conductive dedening members, tuning means for said cavities comprising adjustable conductive end members, a conductive member intermediate the first mentioned members and connected to said grid and extending in one direction to engage an end wall and extending towards but not engaging the other end wall thereby constituting a re-entrant coupling path between the anode-grid and the grid-cathode circuits of said discharge device,

said rst mentioned members being restricted within the vicinity of said electric discharge device in order to compensate for the capacitance effects thereof so that said cavities aiord a substantially uniform impedance to electromagnetic Waves of a predetermined frequency along the longitudinal axes of the cavities, and output electrode means associated with at least one of said cavities.

15. A space resonant system comprising a pair of space resonant. cavities dened by two adjacent sections of a dielectric wave guide of the hollow-pipe type including outer defining members and having throughout an appreciable length thereof an intermediate boundary of the reentrant type, said intermediate boundary being provided with an' aperture, an electric discharge device positioned within said aperture and comprising a plurality of enclosed electrodes including an anode, a cathode and a grid, said grid being connected to said intermediate boundary and said anode and cathode being connected for high frequency currents to respective points on said outer members located substantially along the axis of said aperture which is perpendicular to the longitudinal axis of said cavities, means for restricting the transverse dimensions of said cavities in the'vicinity of said electric discharge device to compensate for the capacitance effect thereof, and means for applying a difference of 

